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Aviation History
1982
1982 - 2276.PDF
DEFENCE Lubrication check on Chinooks Chinook operators are being asked to check helicopter transmissions after US Army investigators uncovered a suspected loss of lubrication in the forward gearbox of the CH-47C which crashed at Mannheim. Lubrication jets were found to be blocked by a grease-like substance, and a bearing may have seized as a result. Boeing has recommended that forward, aft, and comibineir gearboxes be given a once-only inspec tion, and has offered techni cal assistance. The pilot of the Mannheim Chinook asked for permission to land after a transmission chip-detector warning light illuminated soon after take off. Before the helicopter could land, the rotors ap peared to strike each other: forward and aft rotor sys tems overlap by about 60 per cent of blade length. The subsequent loss of a blade, reported by eye-witnesses, may have resulted in the sud den and catastrophic failure of the rear rotor system. The Chinook crashed, killing all 46 on board. According to operators there should be no grease in Chinook transmissions. It has not yet been established whether its presence is re lated to manufacturing or maintenance errors. There are three totally separate lub rication systems for forward, aft, and combiner gearboxes, so that contamination can not be propagated. All Chinook gearboxes have a run-dry capability, but the transmission concerned had been in place for some time without any evidence of a lubrication problem. The latest D-model Chinooks for the US Army, and commer cial versions, have an auxili ary lubrication system and extended run-dry capability. Forward and aft rotor sys tems are synchronised by rigid driveshafts from the combiner gearbox, which accepts power from the two engines, to the respective transmissions mounted with in the rotor pylons. Even in the event of gearbox prob lems these shafts should keep the rotors in phase. Should the rotors dephiase and strike each other, the result would be rapid and catastrophic. Each blade weighs about 3501b and rotates at between 400 and 500 m.p.h. The loss of one blade out of three would set up a violent out-of-balance force of several tons, which would tear the rotor out by its roots. The effect would be particularly severe on the rear system, which has a low- set gearbox driving through a long vertical shaft. A photograph taken just before the Mannheim Chin ook crashed shows that the rear pylon had disintegrated and that the rear rotor was missing. The forward rotor was damaged, and one blade may have been missing. It is extremely unlikely that a rotor could have be come detached. The hub is stressed to operate at up to 300 r.p.m. and normal rotor speed is 235 r.p.m. It is pos sible that, when the forward transmission seized, the syn chronisation shaft may have failed, allowing the rotors to strike each other. Rotor dephasing is virtu ally unheard of in Chinooks, and the US Army, with the world's largest and most di verse helicopter fleet, con siders the CH-47 to be its safest machine. The Army declines to comment on Boeing's action until its acci dent investigation is com plete. Soon after the crash, the Service grounded all of its CH-47Cs. Canada, which operates a similar model, followed suit. Boeing's in spection order covers all Chinook types, however, in cluding those operated by British Airways Helicopters. Finland has received the first of three special mission Learjet 35As equipped for sea patrol, aerial mapping, cargo, ambulance, and rescue duties- The principal role is target-towing for Finnish Hawk trainers. Underwing hardpoints are fitted, and a 360" search radar No decision on Indian Jaguars NEW DELHI The Indian Ministry of De fence has denied reports that local production of the Jag uar strike aircraft is to be cut back. Plans for licence- manufacture of 65 Jaguars have been under review, but no decision has been taken, says the Indian MoD. Local press reports had suggested that as few as 21 Jaguars might be built, but a decision is not expected for at least another month. British Aerospace has com pleted all 40 Jaguars cov ered by the first phase of the £1,000 million deal, and the last five were scheduled to have been ferried to India over the past few days. De livery of knock-down sub assemblies for a further 45 Jaguars continues, and licen see Hindustan Aeronautics (HAL) has flown two locally assembled aircraft. HAL chairman B. K. Ka- pur confirms that his com pany delivered one Jaguar to the Indian Air Force in the last financial year and plans to hand over three this year. The proposed production rate is one-and-a-half-to-two aircraft a month. Kapur is confident that Jaguar pro duction will continue beyond the initial 85 aircraft. Bahrain orders Tigershark WASHINGTON D.C. Bahrain has ordered four Northrop Tigersharks, but the order is not sufficient to launch production of the ex port fighter, the manufac turer says. Northrop delayed its production plans earlier this year after experiencing difficulty getting US Govern ment support for sales. FLIGHT International, 2 October 1982
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